Vibrio cholerae is the causative agent of the diarrheal disease cholera. Many Vibrio
species secrete antimicrobial factors, though the identity of such a factor has not been determined
for any V. cholerae strain. Such an antimicrobial factor could be relevant to pathogenesis of
cholera, which disrupts the intestinal microbiome. In this study, we investigated the antimicrobial effects of supernatant from 72 hour old
cultures of V. cholerae C6706 on Shigella flexneri CFS100. Inhibition of S. flexneri growth was
found to be dependent on the alkaline pH of the supernatant. A 1:1 mixture of pH-adjusted
supernatant and LB was found to inhibit S. flexneri growth at alkaline but not neutral pH, as was
pH-adjusted LB alone. In minimal medium, elevation of supernatant pH by V. cholerae was
dependent on nutritional factors, and this elevation of medium pH also correlated with increased
S. flexneri growth inhibition. Though medium alkalization in LB is often attributed to amino acid
catabolism and the consequent production of ammonia, supplementation of V. cholerae cultures
in minimal medium with amino acids had a weaker effect on alkalization and inhibition than did
supplementation with selected carbon sources. This suggests that some feature of carbon
metabolism causes medium alkalization and the resultant antimicrobial activity. Several V.
cholerae mutants in potentially relevant pathways were screened for alkalization and S. flexneri
growth inhibition, but none had any effect.Complicating this picture is the finding that V. cholerae grown under microaerobic
conditions produce a less alkaline supernatant with stronger S. flexneri growth inhibition. The
significance of this is unknown.Molecular Bioscience
